Because of their physical properties, ceramics can be good candidates for use in the construction of high-quality pre-shaped dental restorations. Aluminum oxide (sometimes referred to as “alumina”) and zirconium oxide (sometimes referred to as “zirconia”) ceramics have been used in the dental field because of their physical and aesthetic properties.
In some existing systems, ceramic dental restorations can be produced by means of a computer-aided design (CAD) system that function in conjunction with a computer-integrated manufacturing (CIM) system. Such a CIM system is available, for example, under the trade designation LAVA™ from 3M ESPE AG (Seefeld, Germany). The CAD system can be coupled to an optical scanner and a numerically-controlled (NC)-milling machine. The optical scanner can be configured to capture a three-dimensional surface of a dentition impression and send the captured data to the CAD system. With the CAD system, a user can modify the surface data as desired, calculate computer numerically-controlled (CNC) data from the shape data using computer-aided manufacturing (CAM) software, and then send the corresponding CNC data to the NC-milling machine. The NC-milling machine can then mill a zirconium oxide (or zirconia) ceramic blank in an as precise as possible agreement with the shape data. Finally, the milled ceramic blank can be sintered, for example, in a sintering furnace.
During the sintering process, the ceramic material generally shrinks a certain amount. In some systems, ceramic dental restorations (e.g., bridge frameworks) can be positioned on pegs, pins or rods (e.g., formed of alumina), or suspended from hangers (e.g., formed from a platinum alloy) during sintering. Such pegs, pins, rods, or hangers can be placed on a honeycomb-like sintering tray in order to accommodate the dental restoration geometry. Such an arrangement allows for any linear movement of the dental restoration that may be induced by shrinkage. In other systems, ceramic dental restorations can be placed on ceramic beads or balls, or on ceramic bulk material, which can then be placed in or on a container or support for sintering.